Catalytic Photooxidation of Pentachlorophenol Using Semiconductor Nanoclusters

Pentachlorophenol (PCP) is a toxic chlorinated aromatic molecule widely used as a fungicide, a bactericide, and a wood preservation, and thus is ubiquitous in the environment. We report photooxidation of PCP using a variety of nanosize semiconductor metal oxides and sulfides in both aqueous and polar organic solvents and compare the photooxidation kinetics of these nanoclusters to widely studied bulk powders such as Degussa P25 TiO 2 and CdS. We study both the light- intensity dependence of PCP photooxidation for nanosize SnO 2 and the size dependence of PCP photooxidation for both nanosize SnO 2 and MoS 2 . We find an extremely strong size dependence for the latter which we attribute to its size-dependent band gap and the associated change in redox potentials due to quantum confinement of the hole−electron pair. We show that nanosize MoS 2 with a diameter of d = 3.0 nm and an absorbance edge of ∼450 nm is a very effective photooxidation catalyst for complete PCP mineralization, even when using only visible-light irradiation.